Use official emsdk bazel toolchain

.bazelrc

@@ -6,22 +6,35 @@
 # editor's search path.
 build --symlink_prefix=dist/
 
-# Use our custom-configured c++ toolchain.
-build:wasm --crosstool_top=//toolchain:emscripten
+# These compile flags are active no matter which build mode we are in
+# (dbg vs opt). For flags specific to build mode, see cc_toolchain_config.bzl.
+build --cxxopt="-std=c++11"
+build --cxxopt="-fno-rtti"
+build --cxxopt="-fno-exceptions"
+build --cxxopt="-fomit-frame-pointer"
 
-# Use --cpu as a differentiator.
-build:wasm --cpu=wasm
+# Remote cache config. Users can add credentials in their .bazelrc.user files.
+build:remote --remote_cache=https://storage.googleapis.com/bazel-remote-cache-tfjs
 
-# Use the default C++ toolchain to build the tools used during the build.
-build:wasm --host_crosstool_top=@bazel_tools//tools/cpp:toolchain
+# Config for Google Cloud continuous integration that uses default credentials.
+build:ci --config=remote
+build:ci --google_default_credentials
 
-# These compile flags are active no matter which build mode we are in
-# (dbg vs opt). For flags specific to build mode, see cc_toolchain_config.bzl.
-build:wasm --cxxopt="-std=c++11"
-build:wasm --cxxopt="-fno-rtti"
-build:wasm --cxxopt="-fno-exceptions"
-build:wasm --cxxopt="-fomit-frame-pointer"
+# This flag is needed to so that the bazel cache is not invalidated
+# when running bazel via `yarn bazel`.
+# See https://github.com/angular/angular/issues/27514.
+build --incompatible_strict_action_env
+run --incompatible_strict_action_env
+
+# Don't use a sandboxed build since it hurts performance.
+# When sandboxed, the wasm backend takes hours to build on a 32 core machine.
+build --spawn_strategy=worker,local
 
-# Disable sandbox environment because emsdk caches files by writing to
-# home directory.
-build:wasm --spawn_strategy=local
+# Load any settings specific to the current user.
+# .bazelrc.user should appear in .gitignore so that settings are not shared with
+# team members. This needs to be last statement in this config, as the user
+# configuration should be able to overwrite flags from this file.
+# See https://docs.bazel.build/versions/master/best-practices.html#bazelrc
+# (Note that we use .bazelrc.user so the file appears next to .bazelrc in
+# directory listing, rather than user.bazelrc as suggested in the Bazel docs).
+try-import %workspace%/.bazelrc.user

.gitignore

@@ -59,4 +59,7 @@ tfjs-backend-wasm/wasm-out/*.js
 tfjs-backend-wasm/wasm-out/*.wasm
 yalc.lock
 yarn-error.log
-cloudbuild_generated.yml
+cloudbuild_generated.yml
+
+# User-specific .bazelrc
+.bazelrc.user

WORKSPACE

@@ -12,18 +12,33 @@ yarn_install(
     yarn_lock = "//:yarn.lock",
 )
 
-# Make all files under $HOME/emsdk/* visible to the toolchain. The files are
-# available as external/emsdk/emsdk/*
-load("//toolchain:cc_toolchain_config.bzl", "emsdk_configure")
-emsdk_configure(name = "emsdk")
+# npm_install used for emscripten dependencies
+load("@build_bazel_rules_nodejs//:index.bzl", "npm_install")
+
+# emscripten 2.0.14
+http_archive(
+    name = "emscripten",
+    sha256 = "e466cd47ddd4bf0acd645412fdf08eda6d232484e48e5a2643e08062a7a4cf56",
+    strip_prefix = "install",
+    url = "https://storage.googleapis.com/webassembly/emscripten-releases-builds/linux/fc5562126762ab26c4757147a3b4c24e85a7289e/wasm-binaries.tbz2",
+    build_file = "//emscripten_toolchain:emscripten.BUILD",
+    type = "tar.bz2",
+)
+
+# Install emscripten dependencies
+npm_install(
+    name = "emsdk_npm",
+    package_json = "@emscripten//:emscripten/package.json",
+    package_lock_json = "@emscripten//:emscripten/package-lock.json",
+)
 
 load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")
 # xnnpack used for fast vectorized wasm operations
 git_repository(
     name = "xnnpack",
-    commit = "55d53a4e7079d38e90acd75dd9e4f9e781d2da35",
+    commit = "f69ac5d218a4f2a68bc2981d61603d43966e8068",
     remote = "https://github.com/google/XNNPACK.git",
-    shallow_since = "1614036677 -0800",
+    shallow_since = "1614818900 -0800",
 )
 
 # The libraries below are transitive dependencies of XNNPACK that we need to

emscripten_toolchain/BUILD.bazel

@@ -0,0 +1,80 @@
+load(":crosstool.bzl", "emscripten_cc_toolchain_config_rule")
+
+package(default_visibility = ["//visibility:public"])
+
+filegroup(
+    name = "common-script-includes",
+    srcs = [
+        "emar.sh",
+        "emcc.sh",
+        "emscripten_config",
+        "env.sh",
+        "@emscripten//:all",
+        "@nodejs//:node_files",
+        "@emsdk_npm//:node_modules",
+    ],
+)
+
+filegroup(
+    name = "compile-emscripten",
+    srcs = [":common-script-includes"],
+)
+
+filegroup(
+    name = "link-emscripten",
+    srcs = [
+        "emcc_link.sh",
+        "link_wrapper.py",
+        ":common-script-includes",
+        "@emscripten//:all",
+        "@nodejs//:node_files",
+    ],
+)
+
+filegroup(
+    name = "every-file",
+    srcs = [
+        ":compile-emscripten",
+        ":link-emscripten",
+        "@emscripten//:all",
+        "@nodejs//:node_files",
+    ],
+)
+
+filegroup(name = "empty")
+
+# dlmalloc.bc is implictly added by the emscripten toolchain
+cc_library(name = "malloc")
+
+emscripten_cc_toolchain_config_rule(
+    name = "wasm",
+    cpu = "wasm",
+    emscripten_version = "emscripten",
+)
+
+cc_toolchain(
+    name = "cc-compiler-wasm",
+    all_files = ":every-file",
+    ar_files = ":common-script-includes",
+    as_files = ":empty",
+    compiler_files = ":compile-emscripten",
+    dwp_files = ":empty",
+    linker_files = ":link-emscripten",
+    objcopy_files = ":empty",
+    strip_files = ":empty",
+    toolchain_config = "wasm",
+    toolchain_identifier = "emscripten-wasm",
+)
+
+cc_toolchain_suite(
+    name = "everything",
+    toolchains = {
+        "wasm": ":cc-compiler-wasm",
+        "wasm|emscripten": ":cc-compiler-wasm",
+    },
+)
+
+py_binary(
+    name = "wasm_binary",
+    srcs = ["wasm_binary.py"],
+)